This invention relates to an oleodynamic control device for steering wheels of vehicles provided with straight traveling stabilizer. More particularly, the invention relates to an oleodynamic control device for steering rear wheels acted upon by a straight traveling stabilizer and a hydraulic steering actuator through an articulated arm.
In some patents rear wheel steering systems are described, particularly for industrial vehicles, in which such pivotable wheels are subjected both to the action of a straight traveling stabilizer and a hydraulic actuator cylinder which exerts forces for modifying the straight traveling condition imposed by the stabilizer to thus determine steering of the wheels.
Swiss Pat. No. 396,652 relates to such a system which comprises a double-acting hydraulic cylinder which through a double fluid conduit controls a steering actuator cylinder. In a straight traveling situation the piston of the control cylinder occupies a position exactly in the center of the cylinder and is connected to the steering system of the vehicle so that each variation from straight traveling causes the piston to shift from said center position, which causes actuation of the actuator cylinder and steering of the wheels. As in such a system the hydraulic circuit which communicates with the control cylinder and the actuator cylinder is always under pressure, there being even provided accumulator means for maintaining a certain value of such pressure, it happens that the least variation of the main steering system from the straight traveling attitude causes steering of the rear wheels. The same effect occurs when there is some play in the connection between the piston of the control cylinder and the main steering system or when use and wear of the piston cause fluid to leak into said cylinder or when there is an imperfect setting of the mechanical members involved in the transmission of movement to the piston. In all these cases, which are practically unavoidable, the system in question exhibits the serious disadvantage of causing undesired steering of the rear wheels with the obvious consequences of side skidding and the risk of coming off the road. This is a serious drawback considering that there are always small oscillations in the main steering system when the vehicle is running at high speed so that in this case undesired steering of the rear wheels is dangerous.
Another system for steering pivotable wheels with straight traveling stabilizer and hydraulic actuator is described in Italian Patent Application No. 68427-A/81 filed Nov. 5, 1981 by the same Applicant. Although this system does not include accumulator means for maintaining a high pressure in the hydraulic circuit, as described in Swiss Pat. No. 396,652, it is open to the same type of criticism as its control cylinder also causes undesired steering of the wheels in the situation outlined above.
It is therefore an object of the present invention to eliminate the disadvantages of the known systems described above and to provide an oleodynamic control device for steering pivotable wheels subject to the action of a straight traveling stabilizer, which will ensure straight traveling stabilization of such wheels even during small steering movements of the main steering system and will also ensure stabilization when play develops in the connection between the control member and the main steering system.